Moving slowly down the west coast, the troops of the Australian II Corps began to encounter large numbers of Japanese army units. The 25th Battalion was given the task of crossing the Puriata River and testing the resolve of the enemy. This major water obstacle was a key part of the Japanese defensive strategy. A strong assault against the 25th left it encircled and in serious trouble. A call for help was put out to the only Australian armoured unit on the island. The use of armour on Bougainville was restricted by a lack of good roads and the many rivers, especially on the drive south towards the key town of Buin. Escorted by infantry, the tanks, in action for the first time, cut a path towards the Puriata.